The agency is charged with handling creative, media planning and buying, as well as affiliate marketing for Moneysupermarket.com.
There was no incumbent on the account, and TBG was appointed without a pitch.
The site enables consumers to compare financial deals on products such as credit cards, loans and mortgages, and its sister website, Travelsupermarket.com.
Earlier this year, Moneysupermarket.com hired Doner Cardwell Hawkins to create its first TV ad campaign.
TBG was founded in 2001 by its managing director, Simon Mansell, and offers a full digital service, including creative, strategy, media planning and technology.
The Moneysupermarket.com win adds to its financial clients, which also include American Express and Ocean Finance. Other brands it works on are DatingDirect and Littlewoods.